1. Field Of The Invention
This invention relates generally to retrievable fluid control valves for controlling fluid flow through a tubing string of a well.
2. Description Of The Prior Art
In the petroleum industry, there is often a need to pump fluids down a tubing string into a subsurface formation of a well. Such fluids are used for a variety of purposes including fracturing, scale removal, chemical treatments, acidizing, and the like.
In many situations, when performing such treating operations on a well it is desirable to control the amount of fluid pumped into the formation. For example, when using expensive chemicals for treatment, it may be desired to minimize the volume of the chemical lost in the well. This is accomplished with valves known as retrievable fluid control valves which are used with a seating nipple at or near the lowest joint of tubing in the well. This type of valve is also useful in protecting weak formations from treating fluids under hydrostatic pressure. These valves can be preset to open and close at specific tubing pressures to allow controlled pumping of fluid into the formation.
U.S. Pat. No. 3,847,223 to Scott et al., and assigned to the assignee of the present invention, discloses such a retrievable fluid control valve having a spring biased valve member which opens in response to a differential pressure created across an annular piston associated with the valve member.
Further developments in such retrievable fluid control valves are shown in U.S. Pat. No. 4,586,569 to Hyde, also assigned to the assignee of the present invention. The Hyde patent discloses a retrievable fluid control valve having a plurality of individually adjustable springs which are connected in mechanical parallel thus providing an adjustable biasing spring for the valve.
Operating experience with retrievable fluid control valves such as those shown in the Hyde '569 patent have shown that there are sometimes problems associated with the valve and seat. The most frequently encountered problem is breakage of the valve or the valve seat. The present invention is directed to an improvement for retrievable fluid control valves generally like those shown in the Hyde '569 patent which will minimize, if not completely eliminate, these previously encountered problems of valve and valve seat breakage.